Re: Storing Video's or vedio file in DB.

I wouldn't even store it on the filesystem if I could avoid that.
Most people I know will assign the video a unique identifier (which is stored in the database) and then store the video file with a 3rd party (e.g. Amazon S3).

1. This is often cheaper.  Videos take up a lot of disk space.  Having to ensure 2-3 copies of a file as a failover is not fun.
2. It offloads work from internal servers.  Why deal with connections that are serving a static file if you can avoid it?

In terms of FS vs DB (aside from the open vs streaming which was already brought up)

I think the big issue with storing large files in the database is the input/output connection.
Postgres has a specified number of max connections available, and each one has some overhead to operate. Meanwhile, a server like nginx can handle 10k connections easily, and with little or no overhead.  While the speed is comparable to the OS, you end up using a resource from a limited database connection pool.  And you run the risk of a slow/dropped client tying up the connection.  
Why allocate a resource to these operations, when there are more lightweight alternatives that won't tie up a database connection ?